Depletion of coagulation factor XII ameliorates brain pathology and cognitive impairment in Alzheimer disease mice

Targeting factor XIIa for therapeutic interference with hereditary angioedema

Hereditary angioedema (HAE) is a rare, potentially life-threatening genetic disorder characterized by recurrent attacks of swelling. Local vasodilation and vascular leakage are stimulated by the vasoactive peptide bradykinin, which is excessively produced due to dysregulation of the activated factor XII (FXIIa)-driven kallikrein-kinin system. There is a need for novel treatments for HAE that provide greater efficacy, improved quality of life, minimal adverse effects, and reduced treatment burden over current first-line therapies. FXIIa is emerging as an attractive therapeutic target for interference with HAE attacks. In this review, we draw on preclinical, experimental animal, and in vitro studies, providing an overview on targeting FXIIa as the basis for pharmacologic interference in HAE. We highlight that there is a range of FXIIa inhibitors in development for different therapeutic areas. Of these, garadacimab, an FXIIa-targeted inhibitory monoclonal antibody, is the most advanced and has shown potential as a novel long-term prophylactic treatment for patients with HAE in clinical trials. The evidence from these trials is summarized and discussed, and we propose areas for future research where targeting FXIIa may have therapeutic potential beyond HAE.

A multi-ethnic proteomic profiling analysis in Alzheimer's disease identifies the disparities in dysregulation of proteins and pathogenesis

Background

Alzheimer's disease (AD) is the most common type of dementia that affects the elderly population. Lately, blood-based proteomics have been intensively sought in the discovery of AD biomarkers studies due to the capability to link external environmental factors with the development of AD. Demographic differences have been shown to affect the expression of the proteins in different populations which play a vital role in the degeneration of cognitive function.

Method

In this study, a proteomic study focused on Malaysian Chinese and Malay prospects was conducted. Differentially expressed proteins (DEPs) in AD patients and normal controls for Chinese and Malays were identified. Functional enrichment analysis was conducted to further interpret the biological functions and pathways of the DEPs. In addition, a survey investigating behavioural practices among Chinese and Malay participants was conducted to support the results from the proteomic analysis.

Result

The variation of dysregulated proteins identified in Chinese and Malay samples suggested the disparities of pathways involved in this pathological condition for each respective ethnicity. Functional enrichment analysis supported this assumption in understanding the protein-protein interactions of the identified protein signatures and indicate that differentially expressed proteins identified from the Chinese group were significantly enriched with the functional terms related to Aβ/tau protein-related processes, oxidative stress and inflammation whereas neuroinflammation was associated with the Malay group. Besides that, a significant difference in sweet drinks/food intake habits between these two groups implies a relationship between sugar levels and the dysregulation of protein APOA4 in the Malay group. Additional meta-analysis further supported the dysregulation of proteins TF, AHSG, A1BG, APOA4 and C4A among AD groups.

Conclusion

These findings serve as a preliminary understanding in the molecular and demographic studies of AD in a multi-ethnic population.

Proteomics of human platelet lysates and insight from animal studies on platelet protein diffusion to hippocampus upon intranasal administration

Human platelet lysates (HPLs) from allogeneic platelet concentrates (PCs) are biomaterials, which are rich in various trophic factors, increasingly used in regenerative medicine and biotherapy. Understanding how preparation methods influence the HPL protein profile, biological function, and clinical outcomes is crucial. Our study sheds light on the proteomes and functionality of different HPLs, with the aim of advancing their scientifically grounded clinical applications. To achieve this, PCs suspended in plasma underwent three distinct processing methods, resulting in seven HPL types. We used three characterization techniques: label-free proteomics and tandem mass tag (TMT)-based quantitative proteomics, both before and after the immunodepletion of abundant plasma proteins. Bioinformatic tools assessed the proteome, and western blotting validated our quantitative proteomics data. Subsequent pre-clinical studies with fluorescent labeling and label-free proteomics were used as a proof of concept for brain diffusion. Our findings revealed 1441 proteins detected using the label-free method, 952 proteins from the TMT experiment before and after depletion, and 1114 proteins from the subsequent TMT experiment on depleted HPLs. Most detected proteins were cytoplasmic, playing key roles in catalysis, hemostasis, and immune responses. Notably, the processing methodologies significantly influenced HPL compositions, their canonical pathways, and, consequently, their functionality. Each HPL exhibited specific abundant proteins, providing valuable insight for tailored clinical applications. Immunoblotting results for selected proteins corroborated our quantitative proteomics data. The diffusion and differential effects to the hippocampus of a neuroprotective HPL administered intranasally to mice were demonstrated. This proteomics study advances our understanding of HPLs, suggesting ways to standardize and customize their production for better clinical efficacy in regenerative medicine and biotherapy. Proteomic analyses also offered objective evidence that HPPL, upon intranasal delivery, not only effectively diffuses to the hippocampus but also alters protein expression in mice, bolstering its potential as a treatment for memory impairments.

Oral anticoagulants: A plausible new treatment for Alzheimer's disease?

Alzheimer's disease (AD) and cardiovascular disease (CVD) are strongly associated. Both are multifactorial disorders with long asymptomatic phases and similar risk factors. Indeed, CVD signatures such as cerebral microbleeds, micro-infarcts, atherosclerosis, cerebral amyloid angiopathy and a procoagulant state are highly associated with AD. However, AD and CVD co-development and the molecular mechanisms underlying such associations are not understood. Here, we review the evidence regarding the vascular component of AD and clinical studies using anticoagulants that specifically evaluated the development of AD and other dementias. Most studies reported a markedly decreased incidence of composite dementia in anticoagulated patients with atrial fibrillation, with the highest benefit for direct oral anticoagulants. However, sub-analyses by differential dementia diagnosis were scarce and inconclusive. We finally discuss whether anticoagulation could be a plausible preventive/therapeutic approach for AD and, if so, which would be the best drug and strategy to maximize clinical benefit and minimize potential risks. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

Serum proteomic analysis in esophagectomy patients with postoperative delirium: A case-control study

BACKGROUND

Postoperative delirium occurs in up to 80% of patients undergoing esophagectomy. We performed an exploratory proteomic analysis to identify protein pathways that may be associated with delirium post-esophagectomy.

OBJECTIVES

Identify proteins associated with delirium and delirium severity in a younger and higher-risk surgical population.

METHODS

We performed a case-control study using blood samples collected from patients enrolled in a negative, randomized, double-blind clinical trial. English speaking adults aged 18 years or older, undergoing esophagectomy, who had blood samples obtained were included. Cases were defined by a positive delirium screen after surgery while controls were patients with negative delirium assessments. Delirium was assessed using Richmond Agitation Sedation Scale and Confusion Assessment Method for the Intensive Care Unit, and delirium severity was assessed by Delirium Rating Scale-Revised-98. Blood samples were collected pre-operatively and on post-operative day 1, and discovery proteomic analysis was performed. Between-group differences in median abundance ratios were reported using Wilcoxon-Mann-Whitney Odds (WMWodds1) test.

RESULTS

52 (26 cases, 26 controls) patients were included in the study with a mean age of 64 (SD 9.6) years, 1.9% were females and 25% were African American. The median duration of delirium was 1 day (IQR: 1-2), and the median delirium/coma duration was 2.5 days (IQR: 2-4). Two proteins with greater relative abundance ratio in patients with delirium were: Coagulation factor IX (WMWodds: 1.89 95%CI: 1.0-4.2) and mannosyl-oligosaccharide 1,2-alpha-mannosidase (WMWodds: 2.4 95%CI: 1.03-9.9). Protein abundance ratios associated with mean delirium severity at postoperative day 1 were Complement C2 (Spearman rs = -0.31, 95%CI [-0.55, -0.02]) and Mannosyl-oligosaccharide 1,2-alpha-mannosidase (rs = 0.61, 95%CI = [0.29, 0.81]).

CONCLUSIONS

We identified changes in proteins associated with coagulation, inflammation, and protein handling; larger, follow-up studies are needed to confirm our hypothesis-generating findings.

Sex-Specific and Traumatic Brain Injury Effects on Dopamine Receptor Expression in the Hippocampus

Traumatic brain injury (TBI) is a major health concern. Each year, over 50 million individuals worldwide suffer from TBI, and this leads to a number of acute and chronic health issues. These include affective and cognitive impairment, as well as an increased risk of alcohol and drug use. The dopaminergic system, a key component of reward circuitry, has been linked to alcohol and other substance use disorders, and previous research indicates that TBI can induce plasticity within this system. Understanding how TBI modifies the dopaminergic system may offer insights into the heightened substance use and reward-seeking behavior following TBI. The hippocampus, a critical component of the reward circuit, is responsible for encoding and integrating the spatial and salient aspects of rewarding stimuli. This study explored TBI-related changes in neuronal D2 receptor expression within the hippocampus, examining the hypothesis that sex differences exist in both baseline hippocampal D2 receptor expression and its response to TBI. Utilizing D2-expressing tdTomato transgenic male and female mice, we implemented either a sham injury or the lateral fluid percussion injury (FPI) model of TBI and subsequently performed a region-specific quantification of D2 expression in the hippocampus. The results show that male mice exhibit higher baseline hippocampal D2 expression compared to female mice. Additionally, there was a significant interaction effect between sex and injury on the expression of D2 in the hippocampus, particularly in regions of the dentate gyrus. Furthermore, TBI led to significant reductions in hippocampal D2 expression in male mice, while female mice remained mostly unaffected. These results suggest that hippocampal D2 expression varies between male and female mice, with the female dopaminergic system demonstrating less susceptibility to TBI-induced plasticity.

Antiplatelet drugs: Potential therapeutic options for the management of neurodegenerative diseases

The blood platelet plays an important role but often remains under-recognized in several vascular complications and associated diseases. Surprisingly, platelet hyperactivity and hyperaggregability have often been considered the critical risk factors for developing vascular dysfunctions in several neurodegenerative diseases (NDDs) like Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis. In addition, platelet structural and functional impairments promote prothrombotic and proinflammatory environment that can aggravate the progression of several NDDs. These findings provide the rationale for using antiplatelet agents not only to prevent morbidity but also to reduce mortality caused by NDDs. Therefore, we thoroughly review the evidence supporting the potential pleiotropic effects of several novel classes of synthetic antiplatelet drugs, that is, cyclooxygenase inhibitors, adenosine diphosphate receptor antagonists, protease-activated receptor blockers, and glycoprotein IIb/IIIa receptor inhibitors in NDDs. Apart from this, the review also emphasizes the recent developments of selected natural antiplatelet phytochemicals belonging to key classes of plant-based bioactive compounds, including polyphenols, alkaloids, terpenoids, and flavonoids as potential therapeutic candidates in NDDs. We believe that the broad analysis of contemporary strategies and specific approaches for plausible therapeutic treatment for NDDs presented in this review could be helpful for further successful research in this area.

The Venular Side of Cerebral Amyloid Angiopathy: Proof of Concept of a Neglected Issue

Small vessel diseases (SVD) is an umbrella term including several entities affecting small arteries, arterioles, capillaries, and venules in the brain. One of the most relevant and prevalent SVDs is cerebral amyloid angiopathy (CAA), whose pathological hallmark is the deposition of amyloid fragments in the walls of small cortical and leptomeningeal vessels. CAA frequently coexists with Alzheimer's Disease (AD), and both are associated with cerebrovascular events, cognitive impairment, and dementia. CAA and AD share pathophysiological, histopathological and neuroimaging issues. The venular involvement in both diseases has been neglected, although both animal models and human histopathological studies found a deposition of amyloid beta in cortical venules. This review aimed to summarize the available information about venular involvement in CAA, starting from the biological level with the putative pathomechanisms of cerebral damage, passing through the definition of the peculiar angioarchitecture of the human cortex with the functional organization and consequences of cortical arteriolar and venular occlusion, and ending to the hypothesized links between cortical venular involvement and the main neuroimaging markers of the disease.

A possible mechanism for the enhanced toxicity of beta-amyloid protofibrils in Alzheimer's disease

The amyloid-beta peptide (Aβ) is a driver of Alzheimer's disease (AD). Aβ monomers can aggregate and form larger soluble (oligomers/protofibrils) and insoluble (fibrils) forms. There is evidence that Aβ protofibrils are the most toxic form, but the reasons are not known. Consistent with a critical role for this form of Aβ in AD, a recently FDA-approved therapeutic antibody targeted against protofibrils, lecanemab, slows the progression of AD in patients. The plasma contact system, which can promote coagulation and inflammation, has been implicated in AD pathogenesis. This system is activated by Aβ which could lead to vascular and inflammatory pathologies associated with AD. We show here that the contact system is preferentially activated by protofibrils of Aβ. Aβ protofibrils bind to coagulation factor XII and high molecular weight kininogen and accelerate the activation of the system. Furthermore, lecanemab blocks Aβ protofibril activation of the contact system. This work provides a possible mechanism for Aβ protofibril toxicity in AD and why lecanemab is therapeutically effective.

Cellular mechanisms of fibrin (ogen): insight from neurodegenerative diseases

Neurodegenerative diseases are prevalent and currently incurable conditions that progressively impair cognitive, behavioral, and psychiatric functions of the central or peripheral nervous system. Fibrinogen, a macromolecular glycoprotein, plays a crucial role in the inflammatory response and tissue repair in the human body and interacts with various nervous system cells due to its unique molecular structure. Accumulating evidence suggests that fibrinogen deposits in the brains of patients with neurodegenerative diseases. By regulating pathophysiological mechanisms and signaling pathways, fibrinogen can exacerbate the neuro-pathological features of neurodegenerative diseases, while depletion of fibrinogen contributes to the amelioration of cognitive function impairment in patients. This review comprehensively summarizes the molecular mechanisms and biological functions of fibrinogen in central nervous system cells and neurodegenerative diseases, including Alzheimer's disease, Multiple Sclerosis, Parkinson's disease, Vascular dementia, Huntington's disease, and Amyotrophic Lateral Sclerosis. Additionally, we discuss the potential of fibrinogen-related treatments in the management of neurodegenerative disorders.

Vascular Dysfunction in Alzheimer's Disease: Alterations in the Plasma Contact and Fibrinolytic Systems

Alzheimer's disease (AD) is the most common neurodegenerative disease, affecting millions of people worldwide. The classical hallmarks of AD include extracellular beta-amyloid (Aβ) plaques and neurofibrillary tau tangles, although they are often accompanied by various vascular defects. These changes include damage to the vasculature, a decrease in cerebral blood flow, and accumulation of Aβ along vessels, among others. Vascular dysfunction begins early in disease pathogenesis and may contribute to disease progression and cognitive dysfunction. In addition, patients with AD exhibit alterations in the plasma contact system and the fibrinolytic system, two pathways in the blood that regulate clotting and inflammation. Here, we explain the clinical manifestations of vascular deficits in AD. Further, we describe how changes in plasma contact activation and the fibrinolytic system may contribute to vascular dysfunction, inflammation, coagulation, and cognitive impairment in AD. Given this evidence, we propose novel therapies that may, alone or in combination, ameliorate AD progression in patients.

Triazol-1-yl Benzamides Promote Anticoagulant Activity via Inhibition of Factor XIIa

BACKGROUND

Human factor XIIa (FXIIa) is a plasma serine protease that plays a significant role in several physiological and pathological processes. Animal models have revealed an important contribution of FXIIa to thromboembolic diseases. Remarkably, animals and patients with FXII deficiency appear to have normal hemostasis. Thus, FXIIa inhibition may serve as a promising therapeutic strategy to attain safer and more effective anticoagulation. Very few small molecule inhibitors of FXIIa have been reported. We synthesized and investigated a focused library of triazol-1-yl benzamide derivatives for FXIIa inhibition.

METHODS

We chemically synthesized, characterized, and investigated a focused library of triazol- 1-yl benzamide derivatives for FXIIa inhibition. Using a standardized chromogenic substrate hydrolysis assay, the derivatives were evaluated for inhibiting human FXIIa. Their selectivity over other clotting factors was also evaluated using the corresponding substrate hydrolysis assays. The best inhibitor affinity to FXIIa was also determined using fluorescence spectroscopy. Effects on the clotting times (prothrombin time (PT) and activated partial thromboplastin time (APTT)) of human plasma were also studied.

RESULTS

We identified a specific derivative (1) as the most potent inhibitor in this series. The inhibitor exhibited nanomolar binding affinity to FXIIa. It also exhibited significant selectivity against several serine proteases. It also selectively doubled the activated partial thromboplastin time of human plasma.

CONCLUSION

Overall, this work puts forward inhibitor 1 as a potent and selective inhibitor of FXIIa for further development as an anticoagulant.

Dysregulated haemostasis in thrombo-inflammatory disease

Inflammatory disease is often associated with an increased incidence of venous thromboembolism in affected patients, although in most instances, the mechanistic basis for this increased thrombogenicity remains poorly understood. Acute infection, as exemplified by sepsis, malaria and most recently, COVID-19, drives 'immunothrombosis', where the immune defence response to capture and neutralise invading pathogens causes concurrent activation of deleterious prothrombotic cellular and biological responses. Moreover, dysregulated innate and adaptive immune responses in patients with chronic inflammatory conditions, such as inflammatory bowel disease, allergies, and neurodegenerative disorders, are now recognised to occur in parallel with activation of coagulation. In this review, we describe the detailed cellular and biochemical mechanisms that cause inflammation-driven haemostatic dysregulation, including aberrant contact pathway activation, increased tissue factor activity and release, innate immune cell activation and programmed cell death, and T cell-mediated changes in thrombus resolution. In addition, we consider how lifestyle changes increasingly associated with modern life, such as circadian rhythm disruption, chronic stress and old age, are increasingly implicated in unbalancing haemostasis. Finally, we describe the emergence of potential therapies with broad-ranging immunothrombotic functions, and how drug development in this area is challenged by our nascent understanding of the key molecular and cellular parameters that control the shared nodes of proinflammatory and procoagulant pathways. Despite the increasing recognition and understanding of the prothrombotic nature of inflammatory disease, significant challenges remain in effectively managing affected patients, and new therapeutic approaches to curtail the key pathogenic steps in immune response-driven thrombosis are urgently required.

Accumulation of high molecular weight kininogen in the brains of Alzheimer's disease patients may affect microglial function by altering phagocytosis and lysosomal cathepsin activity

Increased activation of the contact system protein high molecular weight kininogen (HK) has been shown in plasma and cerebrospinal fluid of Alzheimer's disease (AD) patients, but its potential role in the brain has not been explored. We assessed HK levels in brain tissue from 20 AD patients and controls and modeled the effects of HK on microglia-like cells in culture. We show increased levels of HK in the hippocampus of AD patients, which colocalized with amyloid beta (Aβ) deposits and activated microglia. Treatment of microglia with HK led to cell clustering and elevated levels of phagocytosed Aβ. We demonstrate that microglia internalize HK and traffic it to lysosomes, which is accompanied by reduced activity of lysosomal cathepsins L and S. Our results suggest that HK accumulation in the AD hippocampus may alter microglial uptake and degradation of Aβ fibrils, possibly contributing to microglial dysfunction in AD.

Blocking domain 6 of high molecular weight kininogen to understand intrinsic clotting mechanisms

Background

The contact system is initiated by factor (F) XII activation and the assembly of high molecular weight kininogen (HK) with either FXI or prekallikrein (PK) on a negatively charged surface. Overactivation of this system contributes to thrombosis and inflammation in numerous diseases. To develop effective therapeutics for contact system disorders, a detailed understanding of this pathway is needed.

Methods

We performed coagulation assays in normal human plasma and various factor-deficient plasmas. To evaluate how HK-mediated PK and FXI activation contributes to coagulation, we used an anti-HK antibody to block access to domain 6 of HK, the region required for efficient activation of PK and FXI.

Results

FXI's binding to HK and its subsequent activation by activated FXII contributes to coagulation. We found that the 3E8 anti-HK antibody can inhibit the binding of FXI or PK to HK, delaying clot formation in human plasma. Our data show that in the absence of FXI, however, PK can substitute for FXI in this process. Addition of activated FXI (FXIa) or activated PK (PKa) abolished the inhibitory effect of 3E8. Moreover, the requirement of HK in intrinsic coagulation can be largely bypassed by adding FXIa. Like FXIa, exogenous PKa shortened the clotting time in HK-deficient plasma, which was not due to feedback activation of FXII.

Conclusions

This study improves our understanding of HK-mediated coagulation and provides an explanation for the absence of bleeding in HK-deficient individuals. 3E8 specifically prevented HK-mediated FXI activation; therefore, it could be used to prevent contact activation-mediated thrombosis without altering hemostasis.

Resetting the circadian clock of Alzheimer’s mice via GLP-1 injection combined with time-restricted feeding

Circadian rhythm disturbances are the most common symptoms during the early onset of AD. Circadian rhythm disorders aggravate the deposition of amyloid plaques in the brains of AD patients. Therefore, improving the circadian rhythm of AD patients might slow down the pathological development of neurodegeneration. Circadian regulation is driven by a master clock in suprachiasmatic nuclei (SCN) and peripheral clock located in peripheral organs. The rhythmic feeding–fasting cycle has been proved to dominant cue to entrain peripheral clocks. We hypothesized that dietary intervention to a certain period of time during the dark phase might entrain the clock and reset the disrupted daily rhythms of AD mice. In this study, exogenous glucagon-like peptide-1 (GLP-1) treatment, time-restricted feeding (TRF), and the combination were used to examine the effect of overall circadian rhythm and neurodegenerative pathogenesis of transgenic AD mice. It was confirmed that GLP-1 administration together with time-restricted feeding improves circadian rhythm of 5 × FAD mice including the physiological rhythm of the activity–rest cycle, feeding–fasting cycle, core body temperature, and hormone secretion. Furthermore, GLP-1 and TRF treatments improved the diurnal metabolic homeostasis, spatial cognition, and learning of 5 × FAD mice. The aberrant expression of clock genes, including Baml1, Clock, and Dbp, was improved in the hypothalamus, and pathological changes in neurodegeneration and neuroinflammation were also observed in AD mice with dual treatment.

Direct Oral Anticoagulants (DOACs) for Therapeutic Targeting of Thrombin, a Key Mediator of Cerebrovascular and Neuronal Dysfunction in Alzheimer's Disease

Although preclinical research and observer studies on patients with atrial fibrillation concluded that direct oral anticoagulants (DOACs) can protect against dementia like Alzheimer's disease (AD), clinical investigation towards therapeutical approval is still pending. DOACs target pathological thrombin, which is, like toxic tau and amyloid-ß proteins (Aß), an early hallmark of AD. Especially in hippocampal and neocortical areas, the release of parenchymal Aß into the blood induces thrombin and proinflammatory bradykinin synthesis by activating factor XII of the contact system. Thrombin promotes platelet aggregation and catalyzes conversion of fibrinogen to fibrin, leading to degradation-resistant, Aß-containing fibrin clots. Together with oligomeric Aß, these clots trigger vessel constriction and cerebral amyloid angiopathy (CAA) with vessel occlusion and hemorrhages, leading to vascular and blood-brain barrier (BBB) dysfunction. As consequences, brain blood flow, perfusion, and supply with oxygen (hypoxia) and nutrients decrease. In parenchymal tissue, hypoxia stimulates Aß synthesis, leading to Aß accumulation, which is further enhanced by BBB-impaired perivascular Aß clearance. Aß trigger neuronal damage and promote tau pathologies. BBB dysfunction enables thrombin and fibrin(ogen) to migrate into parenchymal tissue and to activate glial cells. Inflammation and continued Aß production are the results. Synapses and neurons die, and cognitive abilities are lost. DOACs block thrombin by inhibiting its activity (dabigatran) or production (FXa-inhibitors, e.g., apixaban, rivaroxaban). Therefore, DOAC use could preserve vascular integrity and brain perfusion and, thereby, could counteract vascular-driven neuronal and cognitive decline in AD. A conception for clinical investigation is presented, focused on DOAC treatment of patients with diagnosed AD in early-stage and low risk of major bleeding.

Anti-HK antibody reveals critical roles of a 20-residue HK region for Aβ-induced plasma contact system activation

Alzheimer's disease (AD) is a neurodegenerative disorder and the leading cause of dementia. Vascular abnormalities and neuroinflammation play roles in AD pathogenesis. Plasma contact activation, which leads to fibrin clot formation and bradykinin release, is elevated in many AD patients, likely due to the ability of AD's pathogenic peptide β-amyloid (Aβ) to induce its activation. Since overactivation of this system may be deleterious to AD patients, the development of inhibitors could be beneficial. Here, we show that 3E8, an antibody against a 20-amino acid region of high molecular weight kininogen's (HK) domain 6, inhibits Aβ-induced intrinsic coagulation. Mechanistically, 3E8 inhibits contact system activation by blocking the binding of prekallikrein (PK) and factor XI (FXI) to HK, thereby preventing their activation and the continued activation of factor XII (FXII). The 3E8 antibody can also disassemble HK/PK and HK/FXI complexes in normal human plasma in the absence of a contact system activator due to its strong binding affinity for HK, indicating its prophylactic ability. Furthermore, the binding of Aβ to both FXII and HK is critical for Aβ-mediated contact system activation. These results suggest that a 20-amino acid region of HK's domain 6 plays a critical role in Aβ-induced contact system activation, and this region may provide an effective strategy to inhibit or prevent contact system activation in related disorders.

Targeting hypercoagulation to alleviate Alzheimer's disease progression in metabolic syndrome

INTRODUCTION

Metabolic Syndrome (MetS) constitutes an important risk factor for Alzheimer's disease (AD); however, the mechanism linking these two disorders has not been completely elucidated. Hence, hypercoagulation may account for the missing hallmark connecting MetS and AD. The present review proposes how hemostatic imbalance triggered in MetS advances in the context of AD. MetS causes interruption of insulin signaling and inflammation, inciting insulin resistance in the brain. Subsequently, neuroinflammation and brain endothelial dysfunction are prompted that further intensify the exorbitant infiltration of circulating lipids and platelet aggregation, thereby causing hypercoagulable state, impairing fibrinolysis and eventually inducing prothrombic state in the brain leading to neurodegeneration.

OBJECTIVE

This study aims to understand the role of hypercoagulation in triggering the progression of neurodegeneration in MetS. It also offers a few interventions to prevent the progression of AD in MetS targeting hypercoagulation.

METHODS

Literature studies based on MetS related neurodegeneration, the impact of coagulation on aggravating obesity and AD via the mechanisms of BBB disruption, neuroinflammation, and hypofibrinolysis.

CONCLUSION

The present paper proposes the hypothesis that hypercoagulation might amplify MetS associated insulin resistance, neuroinflammation, BBB disruption, and amyloid beta accumulation which eventually leads to AD.

A Leaky Blood–Brain Barrier to Fibrinogen Contributes to Oxidative Damage in Alzheimer’s Disease

The intactness of blood–brain barrier (BBB) is compromised in Alzheimer’s disease (AD). Importantly, evidence suggests that the perturbation and abnormalities appearing in BBB can manifest early in the progression of the disease. The disruption of BBB allows extravasation of the plasma protein, fibrinogen, to enter brain parenchyma, eliciting immune reactivity and response. The presence of amyloid-β (Aβ) peptide leads to the formation of abnormal aggregates of fibrin resistant to degradation. Furthermore, Aβ deposits act on the contact system of blood coagulation, altering levels of thrombin, fibrin clots and neuroinflammation. The neurovascular unit (NVU) comprises an ensemble of brain cells which interact with infiltrating fibrinogen. In particular, interaction of resident immune cell microglia with fibrinogen, fibrin and Aβ results in the production of reactive oxygen species (ROS), a neurotoxic effector in AD brain. Overall, fibrinogen infiltration through a leaky BBB in AD animal models and in human AD tissue is associated with manifold abnormalities including persistent fibrin aggregation and clots, microglial-mediated production of ROS and diminished viability of neurons and synaptic connectivity. An objective of this review is to better understand how processes associated with BBB leakiness to fibrinogen link vascular pathology with neuronal and synaptic damage in AD.

Role of Neurons and Glia Cells in Wound Healing as a Novel Perspective Considering Platelet as a Conventional Player

Wound healing is a complex physiological process in which the damaged or injured tissue is replaced or regenerated by new cells or existing cells respectively in their synthesized and secreted matrices. Several cells modulate the process of wound healing including macrophages, fibroblasts, and keratinocytes. Apart from these cells, platelet has been considered as a major cellular fragment to be involved in wound healing at several stages by secreting its granular contents including growth factors, thus resulting in coagulation, inflammation, and angiogenesis. A distant cell, which is gaining significant attention nowadays due to its resemblance with platelet in several aspects, is the neuron. Not only neurons but also glia cells are also confirmed to regulate wound healing at different stages in an orchestrated manner. Furthermore, these neurons and glia cells mediate wound healing inducing tissue repair and regeneration apart from hemostasis, angiogenesis, and inflammation by secreting various growth factors, coagulation molecules, immunomodulatory molecules as well as neurohormones, neuropeptides, and neurotrophins. Therefore, in wound healing platelets, neurons and glia cells not only contribute to tissue repair but are also responsible for establishing the wound microenvironment, thus affecting the proliferation of immune cells, fibroblast, and keratinocytes. Here in this review, we will enlighten the physiological roles of neurons and glia cells in coordination with platelets to understand various cellular and molecular mechanism in brain injury and associated neurocognitive impairments.

Increased Contact System Activation in Mild Cognitive Impairment Patients with Impaired Short-Term Memory

An activated plasma contact system is an abnormality observed in many Alzheimer's disease (AD) patients. Since mild cognitive impairment (MCI) patients often develop AD, we analyzed the status of contact system activation in MCI patients. We found that kallikrein activity, high molecular weight kininogen cleavage, and bradykinin levels- measures of contact system activation- were significantly elevated in MCI patient plasma compared to plasma from age- and education-matched healthy individuals. Changes were more pronounced in MCI patients with impaired short-term recall memory, indicating the possible role of the contact system in early cognitive changes.

Factor XII protects neurons from apoptosis by epidermal and hepatocyte growth factor receptor-dependent mechanisms

BACKGROUND

Factor XII (FXII) is a serine protease that participates in the intrinsic coagulation pathway. Several studies have shown that plasma FXII exerts a deleterious role in cerebral ischemia and traumatic brain injury by promoting thrombo-inflammation. Nevertheless, the impact of FXII on neuronal cell fate remains unknown.

OBJECTIVES

We investigated the role of FXII and FXIIa in neuronal injury and apoptotic cell death.

METHODS

We tested the neuroprotective roles of FXII and FXIIa in an experimental model of neuronal injury induced by stereotaxic intracerebral injection of N-methyl-D-aspartic acid (NMDA) in vivo and in a model of apoptotic death of murine primary neuronal cultures through serum deprivation in vitro.

RESULTS

Here, we found that exogenous FXII and FXIIa reduce brain lesions induced by NMDA injection in vivo. Furthermore, FXII protects cultured neurons from apoptosis through a growth factor--like effect. This mechanism was triggered by direct interaction with epidermal growth factor (EGF) receptor and subsequent activation of this receptor. Interestingly, the "proteolytically" active and two-chain form of FXII, FXIIa, exerts its protective effects by an alternative signaling pathway. FXIIa activates the pro-form of hepatocyte growth factor (HGF) into HGF, which in turn activated the HGF receptor (HGFR) pathway.

CONCLUSION

This study describes two novel mechanisms of action of FXII and identifies neurons as target cells for the protective effects of single and two-chain forms of FXII. Therefore, inhibition of FXII in neurological disorders may have deleterious effects by preventing its beneficial effects on neuronal survival.

Extracellular protein components of amyloid plaques and their roles in Alzheimer's disease pathology

Alzheimer's disease (AD) is pathologically defined by the presence of fibrillar amyloid β (Aβ) peptide in extracellular senile plaques and tau filaments in intracellular neurofibrillary tangles. Extensive research has focused on understanding the assembly mechanisms and neurotoxic effects of Aβ during the last decades but still we only have a brief understanding of the disease associated biological processes. This review highlights the many other constituents that, beside Aβ, are accumulated in the plaques, with the focus on extracellular proteins. All living organisms rely on a delicate network of protein functionality. Deposition of significant amounts of certain proteins in insoluble inclusions will unquestionably lead to disturbances in the network, which may contribute to AD and copathology. This paper provide a comprehensive overview of extracellular proteins that have been shown to interact with Aβ and a discussion of their potential roles in AD pathology. Methods that can expand the knowledge about how the proteins are incorporated in plaques are described. Top-down methods to analyze post-mortem tissue and bottom-up approaches with the potential to provide molecular insights on the organization of plaque-like particles are compared. Finally, a network analysis of Aβ-interacting partners with enriched functional and structural key words is presented.

Alzheimer's disease neuropathology is exacerbated following traumatic brain injury. Neuroprotection by co-administration of nanowired mesenchymal stem cells and cerebrolysin with monoclonal antibodies to amyloid beta peptide

Military personnel are prone to traumatic brain injury (TBI) that is one of the risk factors in developing Alzheimer's disease (AD) at a later stage. TBI induces breakdown of the blood-brain barrier (BBB) to serum proteins into the brain and leads to extravasation of plasma amyloid beta peptide (ΑβP) into the brain fluid compartments causing AD brain pathology. Thus, there is a need to expand our knowledge on the role of TBI in AD. In addition, exploration of the novel roles of nanomedicine in AD and TBI for neuroprotection is the need of the hour. Since stem cells and neurotrophic factors play important roles in TBI and in AD, it is likely that nanodelivery of these agents exert superior neuroprotection in TBI induced exacerbation of AD brain pathology. In this review, these aspects are examined in details based on our own investigations in the light of current scientific literature in the field. Our observations show that TBI exacerbates AD brain pathology and TiO₂ nanowired delivery of mesenchymal stem cells together with cerebrolysin-a balanced composition of several neurotrophic factors and active peptide fragments, and monoclonal antibodies to amyloid beta protein thwarted the development of neuropathology following TBI in AD, not reported earlier.

Factor XII(a) inhibitors: a review of the patent literature

Introduction: Blood coagulation factor XII (FXII) is an emerging and potentially safe drug target, which dysregulation is associated with thrombosis, hereditary angioedema, and (neuro)inflammation. At the same time, FXII-deficiency is practically asymptomatic. Industrial and academic institutions have developed a number of potential therapeutic agents targeting either FXII zymogen or its active form FXIIa for the treatment of thrombotic and inflammatory conditions associated with the activity of this enzyme.Areas covered: A short overview of the FXII(a) structure and function, underlining its suitability as a drug target, is given. The article reviews patents reported over the last three decades on FXII(a)-targeting therapeutic agents. These agents include small molecules, proteins, peptides, oligonucleotides, siRNAs, and monoclonal antibodies.Expert opinion: The performed analysis of patents revealed that many FXII(a) inhibitors are in the early preclinical stage, while several already showed efficacy in vivo animal models of thrombosis, sepsis, hereditary angioedema, and multiple sclerosis. Two anti-FXIIa agents namely tick protein Ir-CPI and monoclonal antibody CSL312 are currently in human clinical trials. The results of these trials and further studies of FXII(a) pathophysiological functions will encourage the development of new FXII(a) inhibitors.

Obstructive Sleep Apnea, Hypercoagulability, and the Blood-Brain Barrier

Obstructive sleep apnea (OSA) is characterized by repeated episodes of intermittent hypoxia (IH) and is recognized as an independent risk factor for vascular diseases that are mediated by a multitude of mechanistic pathophysiological cascades including procoagulant factors. The pro-coagulant state contributes to the development of blood clots and to the increase in the permeability of the blood-brain barrier (BBB). Such alteration of BBB may alter brain function and increase the risk of neurodegenerative diseases. We aim to provide a narrative review of the relationship between the hypercoagulable state, observed in OSA and characterized by increased coagulation factor activity, as well as platelet activation, and the underlying neural dysfunction, as related to disruption of the BBB. We aim to provide a critical overview of the existing evidence about the effect of OSA on the coagulation balance (characterized by increased coagulation factor activity and platelet activation) as on the BBB. Then, we will present the emerging data on the effect of BBB disruption on the risk of underlying neural dysfunction. Finally, we will discuss the potential of OSA therapy on the coagulation balance and the improvement of BBB.

Amelioration of Cognitive and Behavioral Deficits after Traumatic Brain Injury in Coagulation Factor XII Deficient Mice

Based on recent findings that show that depletion of factor XII (FXII) leads to better posttraumatic neurological recovery, we studied the effect of FXII-deficiency on post-traumatic cognitive and behavioral outcomes in female and male mice. In agreement with our previous findings, neurological deficits on day 7 after weight-drop traumatic brain injury (TBI) were significantly reduced in FXII-/- mice compared to wild type (WT) mice. Also, glycoprotein Ib (GPIb)-positive platelet aggregates were more frequent in brain microvasculature of WT than FXII-/- mice 3 months after TBI. Six weeks after TBI, memory for novel object was significantly reduced in both female and male WT but not in FXII-/- mice compared to sham-operated mice. In the setting of automated home-cage monitoring of socially housed mice in IntelliCages, female WT mice but not FXII-/- mice showed decreased exploration and reacted negatively to reward extinction one month after TBI. Since neuroendocrine stress after TBI might contribute to trauma-induced cognitive dysfunction and negative emotional contrast reactions, we measured peripheral corticosterone levels and the ration of heart, lung, and spleen weight to bodyweight. Three months after TBI, plasma corticosterone levels were significantly suppressed in both female and male WT but not in FXII-/- mice, while the relative heart weight increased in males but not in females of both phenotypes when compared to sham-operated mice. Our results indicate that FXII deficiency is associated with efficient post-traumatic behavioral and neuroendocrine recovery.

The contact activation system and vascular factors as alternative targets for Alzheimer's disease therapy

Alzheimer's disease (AD) is the most common neurodegenerative disease, affecting millions of people worldwide. Extracellular beta-amyloid (Aβ) plaques and neurofibrillary tau tangles are classical hallmarks of AD pathology and thus are the prime targets for AD therapeutics. However, approaches to slow or stop AD progression and dementia by reducing Aβ production, neutralizing toxic Aβ aggregates, or inhibiting tau aggregation have been largely unsuccessful in clinical trials. The contribution of dysregulated vascular components and inflammation is evident in AD pathology. Vascular changes are detectable early in AD progression, so treatment of vascular defects along with anti-Aβ/tau therapy could be a successful combination therapeutic strategy for this disease. Here, we explain how vascular dysfunction mechanistically contributes to thrombosis as well as inflammation and neurodegeneration in AD pathogenesis. This review provides evidence that addressing vascular dysfunction in people with AD could be a promising therapeutic strategy.

Alzheimer's Disease-Rationales for Potential Treatment with the Thrombin Inhibitor Dabigatran

Alzheimer's disease (AD) is caused by neurodegenerative, but also vascular and hemostatic changes in the brain. The oral thrombin inhibitor dabigatran, which has been used for over a decade in preventing thromboembolism and has a well-known pharmacokinetic, safety and antidote profile, can be an option to treat vascular dysfunction in early AD, a condition known as cerebral amyloid angiopathy (CAA). Recent results have revealed that amyloid-β proteins (Aβ), thrombin and fibrin play a crucial role in triggering vascular and parenchymal brain abnormalities in CAA. Dabigatran blocks soluble thrombin, thrombin-mediated formation of fibrin and Aβ-containing fibrin clots. These clots are deposited in brain parenchyma and blood vessels in areas of CAA. Fibrin-Aβ deposition causes microvascular constriction, occlusion and hemorrhage, leading to vascular and blood-brain barrier dysfunction. As a result, blood flow, perfusion and oxygen and nutrient supply are chronically reduced, mainly in hippocampal and neocortical brain areas. Dabigatran has the potential to preserve perfusion and oxygen delivery to the brain, and to prevent parenchymal Aβ-, thrombin- and fibrin-triggered inflammatory and neurodegenerative processes, leading to synapse and neuron death, and cognitive decline. Beneficial effects of dabigatran on CAA and AD have recently been shown in preclinical studies and in retrospective observer studies on patients. Therefore, clinical studies are warranted, in order to possibly expand dabigatran approval for repositioning for AD treatment.

Plasminogen Activators in Neurovascular and Neurodegenerative Disorders

The neurovascular unit (NVU) is a dynamic structure assembled by endothelial cells surrounded by a basement membrane, pericytes, astrocytes, microglia and neurons. A carefully coordinated interplay between these cellular and non-cellular components is required to maintain normal neuronal function, and in line with these observations, a growing body of evidence has linked NVU dysfunction to neurodegeneration. Plasminogen activators catalyze the conversion of the zymogen plasminogen into the two-chain protease plasmin, which in turn triggers a plethora of physiological events including wound healing, angiogenesis, cell migration and inflammation. The last four decades of research have revealed that the two mammalian plasminogen activators, tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA), are pivotal regulators of NVU function during physiological and pathological conditions. Here, we will review the most relevant data on their expression and function in the NVU and their role in neurovascular and neurodegenerative disorders.

Complement Activation in the Central Nervous System: A Biophysical Model for Immune Dysregulation in the Disease State

Complement, a feature of the innate immune system that targets pathogens for phagocytic clearance and promotes inflammation, is tightly regulated to prevent damage to host tissue. This regulation is paramount in the central nervous system (CNS) since complement proteins degrade neuronal synapses during development, homeostasis, and neurodegeneration. We propose that dysregulated complement, particularly C1 or C3b, may errantly target synapses for immune-mediated clearance, therefore highlighting regulatory failure as a major potential mediator of neurological disease. First, we explore the mechanics of molecular neuroimmune relationships for the regulatory proteins: Complement Receptor 1, C1-Inhibitor, Factor H, and the CUB-sushi multiple domain family. We propose that biophysical and chemical principles offer clues for understanding mechanisms of dysregulation. Second, we describe anticipated effects to CNS disease processes (particularly Alzheimer's Disease) and nest our ideas within existing basic science, clinical, and epidemiological findings. Finally, we illustrate how the concepts presented within this manuscript provoke new ways of approaching age-old neurodegenerative processes. Every component of this model is testable by straightforward experimentation and highlights the untapped potential of complement dysregulation as a driver of CNS disease. This includes a putative role for complement-based neurotherapeutic agents and companion biomarkers.

β-Amyloid Orchestrates Factor XII and Platelet Activation Leading to Endothelial Dysfunction and Abnormal Fibrinolysis in Alzheimer Disease

Alzheimer disease (AD) is the most common form of dementia in humans. However, to date, the cause of sporadic AD (SAD), which is the most frequent form, is still unknown. Although it has not been possible to determine the origin of this disease, the amyloid hypothesis is one of the most accepted to explain the etiology of AD. This hypothesis proposes that the pathogenesis of AD is derived from the toxic effect produced by the amyloid-β (Aβ) peptide in the brain parenchyma, but it does not make clear how Aβ is capable of producing such damage. Furthermore, it has been observed that SAD is accompanied by disruptions in the vascular system, such as damage to the blood-brain barrier. This facilitates the transfer of some systemic proteins, such as fibrinogen, to the brain parenchyma, where Aβ is abundant. Therefore, this Aβ interacts with fibrinogen, which favors the formation of clots resistant to fibrinolysis, inducing a risk of thrombosis and neuroinflammation. Notably, Aβ is not only of neuronal origin; platelets also contribute to high Aβ production in the circulation. The Aβ present in circulation favors the activation of coagulation factor XII, which leads to the generation of thrombin and bradykinin. In addition to Aβ-induced platelet activation, all these events favor the development of inflammatory processes that cause damage to the brain vasculature. This damage represents the beginning of the toxic effects of Aβ, which supports the amyloid hypothesis. This review addresses the relationship between alterations in the vascular and hemostatic systems caused by Aβ and how both alterations contribute to the progression of SAD.

Plasma contact factors as novel biomarkers for diagnosing Alzheimer's disease

Background

Alzheimer’s disease (AD) is the most common cause of dementia and most of AD patients suffer from vascular abnormalities and neuroinflammation. There is an urgent need to develop novel blood biomarkers capable of diagnosing Alzheimer’s disease (AD) at very early stage. This study was performed to find out new accurate plasma diagnostic biomarkers for AD by investigating a direct relationship between plasma contact system and AD.

Methods

A total 101 of human CSF and plasma samples from normal and AD patients were analyzed. The contact factor activities in plasma were measured with the corresponding specific peptide substrates.

Results

The activities of contact factors (FXIIa, FXIa, plasma kallikrein) and FXa clearly increased and statistically correlated as AD progresses. We present here, for the first time, the FXIIa cut-off scores to as: > 26.3 U/ml for prodromal AD [area under the curve (AUC) = 0.783, p < 0.001] and > 27.2 U/ml for AD dementia (AUC = 0.906, p < 0.001). We also describe the cut-off scores from the ratios of CSF Aβ_1–42 versus the contact factors. Of these, the representative ratio cut-off scores of Aβ_1–42/FXIIa were to be: < 33.8 for prodromal AD (AUC = 0.965, p < 0.001) and < 27.44 for AD dementia (AUC = 1.0, p < 0.001).

Conclusion

The activation of plasma contact system is closely associated with clinical stage of AD, and FXIIa activity as well as the cut-off scores of CSF Aβ_1–42/FXIIa can be used as novel accurate diagnostic AD biomarkers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40364-020-00258-5.

Gut Inflammation Induced by Dextran Sulfate Sodium Exacerbates Amyloid-β Plaque Deposition in the AppNL-G-F Mouse Model of Alzheimer's Disease

BACKGROUND

Although it is known that the brain communicates with the gastrointestinal (GI) tract via the well-established gut-brain axis, the influence exerted by chronic intestinal inflammation on brain changes in Alzheimer's disease (AD) is not fully understood. We hypothesized that increased gut inflammation would alter brain pathology of a mouse model of AD.

OBJECTIVE

Determine whether colitis exacerbates AD-related brain changes.

METHODS

To test this idea, 2% dextran sulfate sodium (DSS) was dissolved in the drinking water and fed ad libitum to male C57BL/6 wild type and AppNL-G-F mice at 6-10 months of age for two cycles of three days each. DSS is a negatively charged sulfated polysaccharide which results in bloody diarrhea and weight loss, changes similar to human inflammatory bowel disease (IBD).

RESULTS

Both wild type and AppNL-G-F mice developed an IBD-like condition. Brain histologic and biochemical assessments demonstrated increased insoluble Aβ1-40/42 levels along with the decreased microglial CD68 immunoreactivity in DSS treated AppNL-G-F mice compared to vehicle treated AppNL-G-F mice.

CONCLUSION

These data demonstrate that intestinal dysfunction is capable of altering plaque deposition and glial immunoreactivity in the brain. This study increases our knowledge of the impact of peripheral inflammation on Aβ deposition via an IBD-like model system.

Alzheimer's Disease and Vascular Aging: JACC Focus Seminar

Alzheimer’s disease, the leading cause of dementia in the elderly, is a neurodegenerative condition characterized by accumulation of amyloid plaques and neurofibrillary tangles in the brain. However, age-related vascular changes accompany or even precede the development of Alzheimer’s pathology, raising the possibility that they may have a pathogenic role. This review provides an appraisal of the alterations in cerebral and systemic vasculature, the heart, and hemostasis that occur in Alzheimer’s disease and their relationships to cognitive impairment. Although the molecular pathogenesis of these alterations remains to be defined, amyloid-β is a likely contributor in the brain as in the heart. Collectively, the evidence suggests that vascular pathology is a likely pathogenic contributor to age-related dementia, including Alzheimer’s disease, inextricably linked to disease onset and progression. Consequently, the contribution of vascular factors should be considered in preventive, diagnostic, and therapeutic approaches to address one of the major health challenges of our time.

Cyclic peptide FXII inhibitor provides safe anticoagulation in a thrombosis model and in artificial lungs

Inhibiting thrombosis without generating bleeding risks is a major challenge in medicine. A promising solution may be the inhibition of coagulation factor XII (FXII), because its knock-out or inhibition in animals reduced thrombosis without causing abnormal bleeding. Herein, we have engineered a macrocyclic peptide inhibitor of activated FXII (FXIIa) with sub-nanomolar activity (K_i = 370 ± 40 pM) and a high stability (t_1/2 > 5 days in plasma), allowing for the preclinical evaluation of a first synthetic FXIIa inhibitor. This 1899 Da molecule, termed FXII900, efficiently blocks FXIIa in mice, rabbits, and pigs. We found that it reduces ferric-chloride-induced experimental thrombosis in mice and suppresses blood coagulation in an extracorporeal membrane oxygenation (ECMO) setting in rabbits, all without increasing the bleeding risk. This shows that FXIIa activity is controllable in vivo with a synthetic inhibitor, and that the inhibitor FXII900 is a promising candidate for safe thromboprotection in acute medical conditions.

Thrombin, a Mediator of Coagulation, Inflammation, and Neurotoxicity at the Neurovascular Interface: Implications for Alzheimer's Disease

The societal burden of Alzheimer’s disease (AD) is staggering, with current estimates suggesting that 50 million people world-wide have AD. Identification of new therapeutic targets is a critical barrier to the development of disease-modifying therapies. A large body of data implicates vascular pathology and cardiovascular risk factors in the development of AD, indicating that there are likely shared pathological mediators. Inflammation plays a role in both cardiovascular disease and AD, and recent evidence has implicated elements of the coagulation system in the regulation of inflammation. In particular, the multifunctional serine protease thrombin has been found to act as a mediator of vascular dysfunction and inflammation in both the periphery and the central nervous system. In the periphery, thrombin contributes to the development of cardiovascular disease, including atherosclerosis and diabetes, by inducing endothelial dysfunction and related inflammation. In the brain, thrombin has been found to act on endothelial cells of the blood brain barrier, microglia, astrocytes, and neurons in a manner that promotes vascular dysfunction, inflammation, and neurodegeneration. Thrombin is elevated in the AD brain, and thrombin signaling has been linked to both tau and amyloid beta, pathological hallmarks of the disease. In AD mouse models, inhibiting thrombin preserves cognition and endothelial function and reduces neuroinflammation. Evidence linking atrial fibrillation with AD and dementia indicates that anticoagulant therapy may reduce the risk of dementia, with targeting thrombin shown to be particularly effective. It is time for “outside-the-box” thinking about how vascular risk factors, such as atherosclerosis and diabetes, as well as the coagulation and inflammatory pathways interact to promote increased AD risk. In this review, we present evidence that thrombin is a convergence point for AD risk factors and as such that thrombin-based therapeutics could target multiple points of AD pathology, including neurodegeneration, vascular activation, and neuroinflammation. The urgent need for disease-modifying drugs in AD demands new thinking about disease pathogenesis and an exploration of novel drug targets, we propose that thrombin inhibition is an innovative tactic in the therapeutic battle against this devastating disease.

Comparison of proteome alterations during aging in the temporal lobe of humans and rhesus macaques

Rhesus macaques are widely used as animal models for studies of the nervous system; however, it is unknown whether the alterations in the protein profile of the brain during aging are conserved between humans and rhesus macaques. In this study, temporal cortex samples from old and young humans (84 vs. 34 years, respectively) or rhesus macaques (20 vs. 6 years, respectively) were subjected to tandem mass tag-labeled proteomic analysis followed by bioinformatic analysis. A total of 3861 homologous pairs of proteins were identified during the aging process. The conservatively upregulated proteins (n = 190) were involved mainly in extracellular matrix (ECM), focal adhesion and coagulation; while, the conservatively downregulated proteins (n = 56) were enriched in ribosome. Network analysis showed that these conservatively regulated proteins interacted with each other with respect to protein synthesis and cytoskeleton-ECM connection. Many proteins in the focal adhesion, blood clotting, complement and coagulation, and cytoplasmic ribosomal protein pathways were regulated in the same direction in human and macaque; while, proteins involved in oligodendrocyte specification and differentiation pathways were downregulated during human aging, and many proteins in the electron transport chain pathway showed differences in the altered expression profiles. Data are available via ProteomeXchange with identifier PXD013597. Our findings suggest similarities in some changes in brain protein profiles during aging both in humans and macaques, although other changes are unique to only one of these species.

Increased plasma bradykinin level is associated with cognitive impairment in Alzheimer's patients

Alzheimer's disease (AD) is characterized by the presence of proteinaceous brain deposits, brain atrophy, vascular dysfunction, and chronic inflammation. Along with cerebral inflammation, peripheral inflammation is also evident in many AD patients. Bradykinin, a proinflammatory plasma peptide, is also linked to AD pathology. For example, bradykinin infusion into the hippocampus causes learning and memory deficits in rats, and blockade of the bradykinin receptor lessens cognitive impairment in AD mouse models. Even though it has been hypothesized that plasma bradykinin could contribute to inflammation in AD, the level of plasma bradykinin and its association with beta-amyloid (Aβ) pathology in AD patients had not been explored. Here, we assessed plasma bradykinin levels in AD patients and age-matched non-demented (ND) control individuals. We found significantly elevated plasma bradykinin levels in AD patients compared to ND subjects. Additionally, changes in plasma bradykinin levels were more profound in many AD patients with severe cognitive impairment, suggesting that peripheral bradykinin could play a role in dementia most likely via inflammation. Bradykinin levels in the cerebrospinal fluid (CSF) were reduced in AD patients and exhibited an inverse correlation with the CSF Aβ40/Aβ42 ratio. We also report that bradykinin interacts with the fibrillar form of Aβ and co-localizes with Aβ plaques in the post-mortem human AD brain. These findings connect the peripheral inflammatory pathway to cerebral abnormalities and identify a novel mechanism of inflammatory pathology in AD.

Relationship between fibrinogen level and its regulatory gene with Alzheimer's disease and vascular dementia

Objective

Methods

Results

Conclusions

Design and characterization of α1-antitrypsin variants for treatment of contact system-driven thromboinflammation

The contact system produces the inflammatory peptide bradykinin and contributes to experimental thrombosis. C1 esterase-inhibitor (C1INH) deficiency or gain-of-function mutations in factor XII (FXII) cause hereditary angioedema, a life-threatening tissue swelling disease. C1INH is a relatively weak contact system enzyme inhibitor. Although α1-antitrypsin (α1AT) does not naturally inhibit contact system enzymes, a human mutation (M358R; α1AT-Pittsburgh) changes it into a powerful broad-spectrum enzyme inhibitor. It blocks the contact system, but also thrombin and activated protein C (APC), making it an unattractive candidate for therapeutic contact system blockade. We adapted the reactive center loop of α1AT-Pittsburgh (AIPR/S) to overcome these obstacles. Two α1AT variants (SMTR/S and SLLR/S) strongly inhibit plasma kallikrein, activated FXII, and plasmin. α1AT-SMTR/S no longer inhibits thrombin, but residually inhibits APC. In contrast, α1AT-SLLR/S residually inhibits thrombin, but no longer APC. Additional modification at the P1' position (S→V) eliminates residual inhibition of thrombin and APC for both variants, while retaining their properties as contact system inhibitors. Both α1AT-SMTR/V and -SLLR/V are superior to C1INH in reducing bradykinin production in plasma. Owing to their capacity to selectively block contact system-driven coagulation, both variants block vascular occlusion in an in vivo model for arterial thrombosis. Furthermore, both variants block acute carrageenan-induced tissue edema in mice. Finally, α1AT-SLLR/V, our most powerful candidate, suppresses epithelial leakage of the gut in a mouse model of colitis. Our findings confirm that redesign of α1AT strongly alters its inhibitory behavior and can be used for the treatment of contact system-mediated thrombosis and inflammation.

An Integrated View on Vascular Dysfunction in Alzheimer's Disease

BACKGROUND

Cerebrovascular disease is a common comorbidity in patients with Alzheimer's disease (AD). It is believed to contribute additively to the cognitive impairment and to lower the threshold for the development of dementia. However, accumulating evidence suggests that dysfunction of the cerebral vasculature and AD neuropathology interact in multiple ways. Vascular processes even proceed AD neuropathology, implicating a causal role in the etiology of AD. Thus, the review aims to provide an integrated view on vascular dysfunction in AD.

SUMMARY

In AD, the cerebral vasculature undergoes pronounced cellular, morphological and structural changes, which alters regulation of blood flow, vascular fluid dynamics and vessel integrity. Stiffening of central blood vessels lead to transmission of excessive pulsatile energy to the brain microvasculature, causing end-organ damage. Moreover, a dysregulated hemostasis and chronic vascular inflammation further impede vascular function, where its mediators interact synergistically. Changes of the cerebral vasculature are triggered and driven by systemic vascular abnormalities that are part of aging, and which can be accelerated and aggravated by cardiovascular diseases. Key Messages: In AD, the cerebral vasculature is the locus where multiple pathogenic processes converge and contribute to cognitive impairment. Understanding the molecular mechanism and pathophysiology of vascular dysfunction in AD and use of vascular blood-based and imaging biomarker in clinical studies may hold promise for future prevention and therapy of the disease.

Anticoagulants for Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a multifactorial syndrome with a plethora of progressive, degenerative changes in the brain parenchyma, but also in the cerebrovascular and hemostatic system. A therapeutic approach for AD is reviewed, which is focused on the role of amyloid-β protein (Aβ) and fibrin in triggering intra-brain vascular dysfunction and connected, cognitive decline. It is proposed that direct oral anticoagulants (DOACs) counteract Aβ-induced pathological alterations in cerebral blood vessels early in AD, a condition, known as cerebral amyloid angiopathy (CAA). By inhibiting thrombin for fibrin formation, anticoagulants can prevent accumulations of proinflammatory thrombin and fibrin, and deposition of degradation-resistant, Aβ-containing fibrin clots. These fibrin-Aβ clots are found in brain parenchyma between neuron cells, and in and around cerebral blood vessels in areas of CAA, leading to decreased cerebral blood flow. Consequently, anticoagulant treatment could reduce hypoperfusion and restricted supply of brain tissue with oxygen and nutrients. Concomitantly, hypoperfusion-enhanced neurodegenerative processes, such as progressive Aβ accumulation via synthesis and reduced perivascular clearance, neuroinflammation, and synapse and neuron cell loss, could be mitigated. Given full cerebral perfusion and reduced Aβ- and fibrin-accumulating and inflammatory milieu, anticoagulants could be able to decrease vascular-driven progression in neurodegenerative and cognitive changes, present in AD, when treated early, therapeutically, or prophylactically.

An antibody against HK blocks Alzheimer's disease peptide β-amyloid-induced bradykinin release in human plasma

Bradykinin is a proinflammatory factor that mediates angioedema and inflammation in many diseases. It is a key player in some types of hereditary angioedema and is involved in septic shock, traumatic injury, Alzheimer's disease (AD), and stroke, among others. Activation of the plasma contact system leads to elevated levels of plasma kallikrein, which cleaves high molecular weight kininogen (HK) to release bradykinin. Drug development for bradykinin-meditated pathologies has focused on designing inhibitors to the enzymes that cleave HK (to prevent bradykinin release) or antagonists of endothelial bradykinin receptors (to prevent downstream bradykinin action). Here we show a strategy to block bradykinin generation by using an HK antibody that binds to HK, preventing its cleavage and subsequent bradykinin release. We show that this antibody blocks dextran sodium sulfate-induced HK cleavage and bradykinin production. Moreover, while the pathogenic AD peptide β-amyloid (Aβ)42 cleaves HK and induces a dramatic increase in bradykinin production, our HK antibody blocked these events from occurring. These results may provide strategies for developing treatments for bradykinin-driven pathologies.

Plasminflammation-An Emerging Pathway to Bradykinin Production

Plasminogen activation is essential for fibrinolysis—the breakdown of fibrin polymers in blood clots. Besides this important function, plasminogen activation participates in a wide variety of inflammatory conditions. One of these conditions is hereditary angioedema (HAE), a rare disease with characteristic attacks of aggressive tissue swelling due to unregulated production and activity of the inflammatory mediator bradykinin. Plasmin was already implicated in this disease decades ago, but a series of recent discoveries have made it clear that plasmin actively contributes to this pathology. Collective evidence points toward an axis in which the plasminogen activation system and the contact system (which produces bradykinin) are mechanistically coupled. This is amongst others supported by findings in subtypes of HAE that are caused by gain-of-function mutations in the genes that respectively encode factor XII or plasminogen, as well as clinical experience with the antifibrinolytic agents in HAE. The concept of a link between plasminogen activation and the contact system helps us to explain the inflammatory side effects of fibrinolytic therapy, presenting as angioedema or tissue edema. Furthermore, these observations motivate the development and characterization of therapeutic agents that disconnect plasminogen activation from bradykinin production.